An Efficient Production Process Improvement Technique by Simulating In-process Inventory

Abstract

In this paper, a technique for evaluating productivity in a flow shop based on the in-process inventories generated by an unbalance workload is proposed. Using this technique, an efficient improvement strategy can be obtained. There are two kinds of waiting in the production process: the first one is "machining wait", which means the products in the previous process have to wait because the following machining process is busy; and the other one is "arrival wait", which means the workers await the arrival of the product from the previous process. In-process inventory is generated by "machining wait". In most production systems, these two kinds of waiting phenomena have fuzzy characteristics since they are indefinitely or intentionally determined depending on the workers' situations. Considering that the employment of a push system determines these waiting phenomena uniquely, we propose an efficient production process improvement technique. A feature of our technique is that stagnation time in the in-process inventories is introduced as an index to evaluate the efficiency of the production process. The proposed technique is achieved as follows. Firstly, the proposed technique calculates the stagnation time at each process. Secondly, the technique determines the processes that should be improved by priority. Once the improvement of a process is achieved, the same technique is applied to find the next process to be improved. An efficient production system can be designed by repeating these procedures. In order to apply this technique effectively, a program that calculates the stagnation time of the focused production process was developed. This program was used at several medium and small companies in Nagasaki and the productivity was remarkably improved.